In a small bowl, add 2 teaspoons of the salt, 2 teaspoons of the black pepper, and the garlic powder and whisk to combine.
Rub the seasoning mixture over the beef on all sides.
In a medium skillet over medium-high heat, add the oil and heat until it is shimmering.
Add the beef to the hot oil and sear it on all sides, about 2-3 minutes per side.
Transfer the beef to a slow cooker.
Nestle the thyme, the onions, and the bay leaf around the beef in the slow cooker.
Reduce the stovetop heat to medium.
In the same skillet used to sear the beef, add the wine, the Worcestershire sauce, and the garlic cloves and cook, while scraping the bottom of the pan to release the browned bits, until just some of the wine is cooked off, about 1-2 minutes.
Turn off the stovetop heat.
Add the mushrooms, the carrots, and the potatoes to the slow cooker, nestling them around the beef.
Pour the wine mixture and the beef stock over the beef and the vegetables in the slow cooker.
Cover the slow cooker and cook until the beef is very tender, about 8-10 hours on low or 4-5 hours on high.
Optionally, in a medium saucepan over medium-high heat, add about 2 cups of the cooking liquid from the slow cooker and bring it to a boil.
In a small bowl, add the cornstarch and the water and whisk to combine into a slurry.
Add the slurry to the boiling cooking liquid and cook, while stirring, until it thickens into a gravy, about 1 minute.
Transfer the gravy from the heat.
Taste the beef and the gravy for seasoning and add the extra salt and the extra black pepper, as needed.
Plate the beef with the vegetables and drizzle the gravy.
Garnish with the chives and serve.